Apparatus and method for adjusting optical axis for optical wireless communication in free space

Abstract

Provided are an apparatus and method for adjusting an optical axis. In the apparatus, an iris diaphragm and a quadrant photodiode (QPD) are used to align optical axes of an optical system of the apparatus so that optical transmission efficiency between an optical transmitter and an optical receiver can be increased. Since a hole of the iris diaphragm can be adjusted to be small, a beam larger than a light-receiving area of the QPD can be included in the light-receiving area, and optical axis alignment is facilitated accordingly. When the QPD and the iris diaphragm are applied to the apparatus, it is possible to simultaneously perform data transmission, tracking, and optical axis alignment. An optical fiber end surface and optical axes of lenses arranged in parallel are aligned in the apparatus so that alignment between two terminals can be easy and reception efficiency can be increased.

What is claimed is: 
     
       1. An apparatus for adjusting an optical axis for a first terminal and a second terminal which perform optical wireless communication in free space, the first terminal comprising:
 a first light output device configured to output a first light, the second terminal comprising: 
 a second light output device configured to output a second light, 
 the first terminal further comprising: 
 a first iris diaphragm configured to adjust a beam size of the second light from the second light output device of the second terminal; and 
 a first quadrant photodiode (QPD) configured to receive the second light whose beam size has been adjusted by the first iris diaphragm, and 
 the second terminal further comprising: 
 a second iris diaphragm configured to adjust a beam size of the first light from the first light output device of the first terminal; and 
 a second QPD configured to receive the first light whose beam size has been adjusted by the second iris diaphragm, 
 wherein the first iris diaphragm adjusts the beam size of the second light to be smaller than a light-receiving area of the first QPD, 
 wherein the second iris diaphragm adjusts the beam size of the first light to be smaller than a light-receiving area of the second QPD, and 
 wherein the first output device comprises a movable optical fiber connector. 
 
     
     
       2. The apparatus of  claim 1 , wherein the first light output device and the second light output device are optical fiber connectors. 
     
     
       3. The apparatus of  claim 1 , wherein the first terminal further comprises:
 a first stage configured to change a location of the first light output device in a Z direction in which the first light output from the first light output device travels or a direction opposite to the Z direction, and 
 wherein the second terminal further comprises: 
 a second stage configured to change a location of the second light output device in a Z direction in which the second light output from the second light output device travels or a direction opposite to the Z direction. 
 
     
     
       4. The apparatus of  claim 3 ,
 wherein the first stage is a first multi-axis stage which changes the location of the first light output device in at least one of X, Y, pan, and tilt directions in addition to the Z direction on the basis of a location at which the first light output from the first light output device is received by the second QPD, and 
 wherein the second stage is a second multi-axis stage which changes the location of the second light output device in at least one of X, Y, pan, and tilt directions in addition to the Z direction on the basis of a location at which the second light output from the second light output device is received by the first QPD. 
 
     
     
       5. The apparatus of  claim 1 , comprising:
 a first device configured to detect a location of the first light received by the second QPD and visualize coordinates of the location of the first light and 
 a second device configured to detect a location of the second light received by the first QPD and visualize coordinates of the location of the second light. 
 
     
     
       6. The apparatus of  claim 1 , wherein the first terminal further comprises:
 a first lens which passes the first light to the free space and receives the second light from the second terminal, and 
 wherein the second terminal further comprises: 
 a second lens which passes the second light to the free space and receives the first light from the first terminal. 
 
     
     
       7. The apparatus of  claim 1 , wherein the first terminal further comprises:
 a first optical path changer configured to change a path of the second light output from the second light output device toward the first QPD, and 
 wherein the second terminal further comprises: 
 a second optical path changer configured to change a path of the first light output from the first light output device toward the second QPD. 
 
     
     
       8. The apparatus of  claim 1 , wherein the first terminal further comprises:
 a first beam splitter configured to split the first light output from the first light output device, and 
 wherein the second terminal further comprises: 
 a second beam splitter configured to split the second light output from the second light output device. 
 
     
     
       9. A method of adjusting an optical axis for a first terminal and a second terminal which perform optical wireless communication in free space, the method comprising:
 outputting a first light from a first optical fiber end surface of the first terminal; 
 outputting a second light from a second optical fiber end surface of the second terminal; 
 receiving the second light output from the second optical fiber end surface by a first quadrant photodiode (QPD) of the first terminal; 
 receiving the first light output from the first optical fiber end surface by a second QPD of the second terminal; 
 adjusting a beam size of the second light received by the first QPD with a first iris diaphragm of the first terminal; and 
 adjusting a beam size of the first light received by the second QPD with a second iris diaphragm of the second terminal, 
 wherein the first iris diaphragm adjusts the beam size of the second light to be smaller than a light-receiving area of the first QPD, 
 wherein the second iris diaphragm adjusts the beam size of the first light to be smaller than a light-receiving area of the second QPD, and 
 wherein the first optical fiber end surface is comprised in a movable connector. 
 
     
     
       10. The method of  claim 9 , further comprising:
 changing a location of the first optical fiber end surface in a Z direction in which the first light output from the first optical fiber end surface travels or a direction opposite to the Z direction: and 
 changing a location of the second optical fiber end surface in a Z direction in which the second light output from the second optical fiber end surface travels or a direction opposite to the Z direction. 
 
     
     
       11. The method of  claim 10 , wherein the changing of the location of the first optical fiber end surface comprises:
 changing the location of the first optical fiber end surface in at least one of X, Y, pan, and tilt directions in addition to the Z direction and the direction opposite to the Z direction, and 
 wherein the changing of the location of the second optical fiber end surface comprises: 
 changing the location of the second optical fiber end surface in at least one of X, Y, pan, and tilt directions in addition to the Z direction and the direction opposite to the Z direction. 
 
     
     
       12. The method of  claim 9 , further comprising:
 detecting a location of the second light received by the first QPD and visualizing coordinates of the location of the second light and 
 detecting a location of the first light received by the second QPD and visualizing coordinates of the location of the first light. 
 
     
     
       13. The method of  claim 9 , further comprising:
 adding a first lens between the first optical fiber end surface and the second QPD and adjusting at least one of pan and tilt of the first lens; and 
 adding a second lens between the second optical fiber end surface and the first QPD and adjusting at least one of pan and tilt of the second lens. 
 
     
     
       14. The method of  claim 9 , further comprising:
 before the first light output from the first optical fiber end surface is received by the second QPD, changing a path of the first light; and 
 before the second light output from the second optical fiber end surface is received by the first QPD, changing a path of the second light. 
 
     
     
       15. The method of  claim 9 , further comprising:
 before the first light output from the first optical fiber end surface is received by the second QPD, splitting the first light; and 
 before the second light output from the second optical fiber end surface is received by the first QPD, splitting the second light.